The conventional photoelectric converter module comprises a photoelectric converter chip which converts an optical signal into an electric signal, a chip carrier which carries the photoelectric converter chip on one side surface thereof, a pre-amplifier which amplifies the electric signal, a hybrid integrated circuit (HIC) board on which the chip carrier and the pre-amplifier are mounted, an optical fiber which supplies an optical signal to the photoelectric converter chip, a lens which focuses a light to the photoelectric converter chip, a lens holder which holds the lens, a package member which houses electric elements such as the chip carrier, the HIC board, etc., and a metal cap which seals the electric elements inside the package member.
The chip carrier is provided with conductor patterns on the side and bottom surfaces, and the photoelectric converter chip is attached on the side surrface to be connected to the conductor patterns. On the other hand, the HIC board is provided with conductor patterns on the top surface thereof. The chip carrier is fixed on the HIC board by soldering with a soldering layer, and the HIC board is fixed on the package member by soldering. The photoelectric converter chip is connected electrically with the pre-amplifier via the conductor patterns of the chip carrier, the soldering layer between the chip carrier and the HIC board, and the conductor patterns of the HIC board.
In operation, an optical signal transmitted through the optical fiber is supplied to the photoelectric converter chip through the lens. Then, the optical signal is converted into an electric signal in the photoelectric converter chip, and then transmitted to the pre-amplifier through the conductor patterns of the chip carrier and the conductor patterns of the HIC board, and then the electric signal is amplified by the pre-amplifier.
In the photoelectric converter module, the frequency characteristic depends on an input impedance of the pre-amplifier, a junction capacity Dj of the photoelectric converter chip, and parasitic capacities Ct of the conductor patterns of the chip carrier, the soldering layer, and the conductor patterns of the HIC board.
A trans-impedance type circuit is generally adopted as the pre-amplifier because of having advantages in frequency range characteristic, receiving sensibility and dynamic range. In the photoelectric converter module which requires to operate in a super high speed transmission over 1 Gb/s, a trans-impedance type circuit comprising a GaAs-MESFET is used as the pre-amplifier in order to realize a high receiving sensibility and a wide range characteristic. In this case, the input impedance of the pre-amplifier is relatively high, so that sensibility of the input capacity is high. As a result, the frequency characteristic in the band of 3 dB down practically depends on an input impedance of the pre-amplifier, the junction capacity Cj of the photoelectric converter chip, and the parasitic capacities Ct of the conductor patterns of the chip carrier, the soldering layer and the conductor patterns of the HIC board.
According to the conventional photoelectric converter module, however, there is a disadvantages in that the photoelectric converter module cannot be used in the frequency range over 3 GHz, because parasitic capacities in the conductor patterns of the HIC board and the soldering layer are large.
Furthermore, there is another disadvantage in that the photoelectric converter module has little reliability because of the deviation of an optical axis between the photoelectric converter chip and the optical system including the lens. The deviation is caused by creeping of the soldering layers, one of which fixes the chip carrier on the HIC board and the other fixes the HIC board on the package member. In the fabrication process of the photoelectric converter module, the photoelectric converter chip, that is a photodiode or an avalanche type photodiode, must be protected from a high temperature, which may cause damage to the photoelectric converter chip. For this purpose, the photoelectric converter chip is fixed on the conductor pattern of the chip carrier, for instance, by soldering of Au-Sn alloy which has a melting point of approximately 280.degree. C. In such a case, the soldering material which is used for fixing the chip carrier on the HIC board and fixing the HIC board on the package member must have a melting point lower than that of Au-Sn alloy to avoid the softening of the Au-Sn alloy solder, resulting in the collapse of the fixing of the photoelectric converter chip on the conductor pattern. As a result, the creeping of the soldering layers may occur, because it tends to occur more often as a melting point thereof lowers.